This invention relates to a new therapeutic use for levobupivacaine or (S)-1-butyl-N-(2,6-dimethylphenyl)-2-piperidinecarboxamide.
Racemic bupivacaine is an effective long-acting local anesthetic, and may be given as an epidural. However, racemic bupivacaine is cardiotoxic, having depressant electrophysiological and mechanical effects on the heart. It should therefore be used with caution in cardiac-compromised patients, and the use of high doses and high concentrations is contraindicated.
In particular, bupivacaine has produced death in a number of patients, including women in childbirth and when used in the Bier""s block technique. Although the incidence of death has been relatively small, the concern has been sufficient to stop the use of 0.75% bupivacaine for obstetrics and the prescribing of bupivacaine for use in Bier""s blocks.
In addition, due to its mode of action, directly on the nervous system, at higher doses bupivacaine is known to have undesirable central nervous system (CNS) side-effects which, prima facie, are connected to its anesthetic activity. Indeed, the occurrence of CNS side-effects is one of the major factors limiting the use of this drug in normal clinical practice employing techniques such as local infiltration, nerve block, field block, epidural and spinal blocks.
It is known that levobupivacaine is probably less cardiotoxic than dexbupivacaine and racemic bupivacaine. See, for example, Vanhoutte et al. (1991) Br. J. Pharmacol. 103:1275-1281, and Denson et al. (1992) Regional Anaesthesia 17:311-316. Vanhoutte et al. studied the effects of bupivacaine enantiomers on the electrophysiological properties of guinea pig isolated papillary muscle; this is based on their statement that xe2x80x9cthe cardiotoxicity of bupivacaine seems to be mainly of electrophysiological origin.xe2x80x9d
Surprisingly, it has now been found that while levobupivacaine retains the anesthetic activity of the racemate, it produces less CNS side-effects, i.e., the CNS side-effects and the anesthetic activity of levobupivacaine are not interrelated in the same manner as in racemic bupivacaine. Expressed in another way, the therapeutic ratio of levobupivacaine with respect to CNS side-effects is unexpectedly higher than it is for the racemic drug. This, coupled with the known reduced cardiac side-effects of levobupivacaine, means that levobupivacaine is useful as a local anesthetic, particularly in clinical procedures where the risk of systemic exposure to the drug is increased, and harmful side-effects are associated therewith. Indeed, it may be useful in any clinical procedure in which the racemic drug has, or may have, a debilitating effect. In addition, while levobupivacaine can be used at doses conventionally used for the racemic drug, it can also be used at higher doses and/or over longer periods, formerly contraindicated for the racemic drug, enabling better anesthesia, e.g., in terms of availability to different patient types, extent of anesthetic block achieved, etc., without the adverse effects conventionally associated with these dose regimens.
According to a first aspect of the present invention, a method of providing anesthesia, in particular without concomitant adverse systemic side-effects (e.g., CNS), in a patient, comprises administering to the patient an effective amount of levobupivacaine.
According to a second aspect of the present invention, a method of providing anesthesia in obstetrics comprises administering to a patient levobupivacaine.
According to a third aspect of the present invention, a pharmaceutical composition comprises a solution, preferably aqueous, having a concentration of greater than 0.75% w/v of levobupivacaine, measured as the free base.
According to a fourth aspect of the present invention, a unit dose of levobupivacaine comprises an ampoule containing the above-described composition.
For the purpose of the present invention, CNS side-effects include effects such as tinnitus, numb tongue or lips, and dry mouth, and are the early indicators of direct nervous system effects. For instance, CNS side-effects are typically used as warnings of the onset of convulsions (which in a pregnant woman may also be induced in utero) which must be avoided because of the risk to the patient, e.g. death, brain damage, foetal distress, etc. As a result, clinical administration of a local anesthetic is stopped upon onset of these early symptoms, whether or not adequate anesthesia or analgesia has been achieved. The dose at which CNS side-effects appear varies greatly between patients and cannot be predicted reliably.
In the method of the present invention, levobupivacaine may be provided in solution, for infusion or injection into the epidural or spinal space, or for administration by any of the conventional means for obtaining a nerve or field block. In addition to the anesthetic blocks conventionally provided by the racemate, levobupivacaine may also be useful in providing blocks in areas of the body where the risk of systemic exposure to the drug, and therefore CNS side-effects, is particularly high. Examples include open wounds and vascular areas, for instance using intercostal blocks for the latter.
Administration of levobupivacaine may be continuous or bolus administration. This may be done using conventional apparatus, e.g., including means for the patient to induce infusion as desired. The daily dose administered to the patient may be in the relatively low range known for the administration of racemic bupivacaine but, because of the decreased CNS side-effects of levobupivacaine, may be higher than the conventional dose for the racemic drug. For instance, the patient may receive a daily dose of levobupivacaine of up to about 2500 mg. However, it is preferred to provide a considerable safety margin for the patient and, therefore, for the patient to receive a daily dose of less than about 2000 mg. Consequently, the total dose of levobupivacaine may be around, or in excess of, about 2 mg per kg of patient body weight.
The concentration of levobupivacaine to be given can be that conventionally used for the racemic drug. However, the concentration is typically higher than this, for instance, at least about 0.75% w/v, and can be up to about 2% w/v. Preferably, however, the concentration of levobupivacaine is in the range of about 0.8% to about 1.5% w/v, and more preferably a concentration of about 1%, 1.25%, or 1.5% w/v is used. The solution is preferably aqueous.
The solution may typically be put up in unit doses of from about 1 to about 15 ml, and preferably of about 10 ml. However, the unit doses may be higher, for example, up to about 40 ml or higher. The unit doses my be in the form of ampoules, which may be made of any suitable material, e.g., glass or an appropriately impervious plastic material. Unit dosages comprising at least about 75 mg, but preferably less than about 200 mg, of levobupivacaine can be administered, and more preferably the unit dosage is in the range of about 80 to about 150 mg. Consequently, the patient may receive a daily dose of levobupivacaine of up to about 2500 mg, but it is preferred that the daily dose is less than about 2000 mg.
The administration of levobupivacaine over a range of concentrations, including those currently used for the racemic drug and the higher concentrations described above, can be carried out for significantly longer periods than at present, again as a result of the reduced CNS side-effects experienced with levobupivacaine. For example, levobupivacaine can be administered to a patient safely for at least 24 hours, often up to 72 hours, and even for periods of up to a week or a fortnight, or longer. It can, of course, be administered for similar periods already used for the racemic drug, e.g., between about 3 and 6 hours.
The method of the present invention is particularly useful in surgical procedures carried out on patients who are cardiac- or CNS-compromised, or patients predisposed to cardiac- or CNS-related conditions, i.e., having a low CNS threshold. Alternatively, the patient may be one in which the direct nervous system effects following CNS side-effects are particularly dangerous, or even lethal, e.g, a pregnant woman, and especially a woman in, or about to start, labour or to undergo Caesarian section.
The levobupivacaine used in the present invention is preferably substantially free of dexbupivacaine, and is more preferably in at least 90%, and most preferably at least 99%, enantiomeric excess with respect to dexbupivacaine. Throughout this specification, reference to bupivacaine and its enantiomers includes pharmaceutically-acceptable salts thereof.